Locking dog leash

What are your thoughts about a locking dog leash like the one described here?
 This locking dog leash allows you to lock your dog safely outside while you are in a store or coffee shop.
 It prevents your dog from being stolen while youre inside.
 It is a standard length leash made of a material that cannot be cut.
 The handle end can be locked to a bench, sign post, tree, fence or other secure structure.
 The other end of the leash locks comfortably and securely around your dogs neck.
 Only you can lock or unlock the leash.

I am looking for just this kind of leash. I want to be able to pop into the grocery store for a few minutes and not worry about a person taking my dog. I live in the city and if anyone were attacking the dog, they would be stopped or at l;east cause enough commotion that I would be able to respond.
I did see one such leash on Ebay but it would have cost over $45 and I did not want to gamble on it working.

No way. If you need to run into the store and leave the dog out leave him/her home. Too many things could happen. How do you know someone would be stopped or enough commotion would be made?? I see such scary stuff every day--all it takes is a second some punk goes by with a skateboard and cracks said dog on the head---the list goes on and on.